It is known to provide articles such as telephone cables, electrical cables, pipelines and the like with a protective covering for sealing and protecting them from adverse conditions such as corrosion and moisture. For example, pipes for pipelines may be provided with an extruded thermoplastic coating, or with a fusion bonded coating.
It is also often desired to provide a second covering having a functional coating on its underside at least partially superimposed on the first-mentioned covering. For example, sometimes the pipeline coating may have a hole or holiday therein which may be patched by applying a covering piece having a functional coating on its underside. As a further example, usually the ends of the pipes are left bare of protective coating to facilitate welding, and this bare section is protected subsequent to welding with a heat shrinkable sleeve, either a cylindrical sleeve or more usually a wrap-around sleeve, which has a functional coating on its inner side and that is shrunk down tightly in contact with the exposed metal and having its ends overlapping the coatings of the adjacent pipe sections.
The lateral stability of the superimposed coverings is not always as great as may be desired, especially when exposed to soil stress. Such soil stress may be encountered by a pipeline or other buried article when the article moves bodily through the soil as a result of, for example fluctuations in the temperature of the conveyed fluid.
It is known to use mastics as the functional coating. The term "mastics" is used herein in the sense in which it is understood by those skilled in the art. As understood by those skilled in the art mastics are generally pressure-sensitive adhesive materials which are somewhat soft and gum-like in nature, and which maintain these properties over a wide range of temperatures. The mastics provide good water resistance, ease of application and less sensitivity to ambient temperature during application but exhibit low shear strengths and poor resistance to soil stress. It is also known to use hot melt adhesives as the functional coatings, or hybrids which combine the properties of mastics and hot melt adhesives. The term "hot melt adhesives" is used herein in the sense in which it is understood by those skilled in the art. As known by those skilled in the art hot melt adhesives are adhesive materials typically having little or no surface tack at working temperatures, but rather relying on having previously achieved a high interface temperature to flow and form a bond with the substrate. Generally, the hybrids and hot melt adhesives have lower water resistance and greater difficulty of application and greater temperature sensitivity than the mastics, but have higher shear strengths and increased resistance to soil stress. However, the resistance to soil stress of even the hybrids and hot melts may still not be as great as is desirable.